1. Field of the Invention
This invention relates to heat-resistant, propylene resin-based molding materials which are excellent in moldability, and which can produce less warped, lightweight molded products having high heat resistance and high strength.
2. Background Art
Molded products obtained from a propylene resin are excellent in mechanical strength, processability and economical efficiency, so that they have been widely used in the field of industrial parts such as automotive parts. Further, in such a field where high rigidity and high heat resistance are especially required, high-performance composite materials composed of a propylene resin and an inorganic filler such as talc or glass fibers have been practically used. Such composite materials have been widely used, for example, for automotive parts, in particular, interior parts such as a trim and an instrument panel, exterior parts such as a bumper, and functional parts such as a fan shroud.
The conventional composite materials composed of a propylene resin and glass fibers possess a high level of heat resistance. However, there is a problem with the conventional composite materials that when they are subjected to injection molding and then cooled, the resulting molded product tends to thermally shrink to warp. As a method for preventing the molded product from warping, it is known to increase the fluidity of the composite molding material. It is also known to additionally use flat-shaped fillers such as talc and mica in the composite molding material. However, these methods are not satisfactory in that the prevention of warping in the molded product is insufficient, or in that the required use of a large amount of filler increases the density of the composition, leading to a heavier molded product.
It is therefore an object of the present invention to provide a propylene resin-based molding material which has high heat resistance and good moldability and which can produce lightweight molded products with very little warping.